Effects such as chorus, flanging, and phasing are well-known examples. Modulation effects typically delay the incoming signal by a few milliseconds and use an LFO to modulate the delayed signal. The LFO may also be used to modulate the delay time in some effects.

A low frequency oscillator (LFO) is much like the sound-generating oscillators in synthesizers, but the frequencies generated by an LFO are so low that they can’t be heard. Therefore, they are used only for modulation purposes. LFO parameters include speed (or frequency) and depth—also called intensity—controls.

You can also control the ratio of the affected (wet) signal and the original (dry) signal. Some modulation effects include feedback parameters, which add part of the effect’s output back into the effect input.

Other modulation effects involve pitch. The most basic type of pitch modulation effect is vibrato. It uses an LFO to modulate the frequency of the sound. Unlike other pitch modulation effects, vibrato alters only the delayed signal.

More complex modulation effects, such as Ensemble, mix several delayed signals with the original signal.